Question

Why are plastic building blocks good for building molecules

Answer 1

Because they're durable and can provide a somewhat accurate visual representation. 

Answer 2

Plastic building blocks are good for building molecules because of some useful properties which they possess. For instance, plastic are flexible, they can be easily manipulated and can be made into any shape, size and combination. They can also be produced using different colors. Because of these features, they can be used to build and to explain how molecules behave.